The Society of Automotive Engineers (SAE) publishes many new, revised, and reaffirmed standards each year in three categories, including Ground Vehicle Standards (J-Reports). Information on these standards is available on the World Wide Web at http://www.sae.org. SAE standard J592 defines a clearance lamp as a lamp mounted on the permanent structure of a vehicle as near as practicable to the upper left and right extreme edges to indicate the overall width and height of the vehicle. The standard also defines a side marker lamp as a lamp which shows to the side of the vehicle, mounted on the permanent structure of the vehicle as near as practicable to the front and rear edges to indicate the overall length of the vehicle. A combination lamp is defined by the standard as a single lamp which simultaneously fulfills the requirements of clearance and side marker lamps. The standard also specifies certain photometric requirements for these lamps, including candela requirements, as well as locations at which the requirements shall be taken relative to the vehicle.
A combination lamp is mounted at a 45.degree. horizontal angle to the direction of travel of the vehicle, and yet must meet the marker lamp visibility requirements to the front and side of the vehicle. A specified amount of light is required to be visible from +90.degree. to -90.degree. relative to the axis of the lamp.
Typically, clearance, side marker and combination lamps used on vehicles use high-intensity incandescent bulbs and optical lenses to meet the photometric requirements. There are several drawbacks to using incandescent bulbs. First, filaments burn out regularly, jeopardizing safety. Secondly, bulbs mounted in sockets are subjected to vibrations which tend to break the filaments and occasionally break the electrical circuit. Finally, incandescent bulbs consume a fair amount of electrical energy, especially when used in large numbers as on a tractor-trailer.
Heretofore, light emitting diodes (LEDs) have not been generally used as clearance, marker or combination lamps. There are two reasons for this. First, LEDs have not traditionally been bright enough for this use. Secondly, LEDs emit light in a narrow cone, and thus require lens optics to distribute the light into a 180.degree. pattern to meet SAE standards.
One example of an apparently successful use of LEDs in clearance and side marker lamps is disclosed in U.S. Pat. No. 5,567,036 (Theobald et al.). This patented invention uses a plurality of LEDs mounted on three circuit boards arranged in three planes, in combination with a lens assembly to spread the light in an approximate arc of 180.degree.. There are several disadvantages associated with this solution to the problem. Mounting LEDs on different circuit boards and in different planes is costly, and can cause the lamp's components to break free during Department of Transportation required vibration tests. Furthermore, encapsulation of components within LED lamps is common, and having LEDs mounted in different planes can make it extremely difficult to encapsulate components without covering the LED body such that light output is affected. Also, lens optics are not especially efficient at redirecting light to extreme angles.
What is needed, then, is an LED combination lamp assembly which meets SAE standards, and yet comprises all LEDs mounted on a single circuit board in a single plane and uses reflectors rather than optics to direct the light where needed to meet the requirements of the standard.